1. Technical Field
The present invention concerns a vector modulator.
2. State of Prior Art
Electrical signal phase shifting may be digital, with phase jumps, or analogue, with continuous phase variation.
Digital phase shifters use PIN-diodes or field effect transistors, used as electronic switches, allowing switching between transmission lines of different lengths (phase shifting by propagation/transmission delay) or else between sections of filtering structures of the low-pass/high-pass type, for example.
The use of varactor diodes or field effect transistors as continuously variable impedances allows analogue phase shifters to be made, providing wave phase shifting in transmission, as in vector modulators, or else in reflection, as in diode phase shifters.
In a diode phase shifter, as shown in FIG. 1, the phase and quadrature outputs of the hybrid coupler 10 are charged by variable reactive elements. The variation in reactive impedance relative to the characteristic impedance (generally 50xcexa9) entails a variation in the phase of the output signal S by means of a complex reflection coefficient {tilde over (xcex93)}.
The following signals are obtained:                               Input          ⁢                      :                                                sin          ⁢                      xe2x80x83                    ⁢                      (                          ω              ⁢                              xe2x80x83                            ⁢              t                        )                                                        Output          ⁢                      xe2x80x83                    ⁢          O          ⁢                      :                                                            Γ            ~                    ⁢                      xe2x80x83                    ⁢          sin          ⁢                      xe2x80x83                    ⁢                      (                          ω              ⁢                              xe2x80x83                            ⁢              t                        )                                                        Output          -                      90            ⁢            xc2x0            ⁢                          :                                                                        -                          Γ              ~                                ⁢                      xe2x80x83                    ⁢          cos          ⁢                      xe2x80x83                    ⁢                      (                          ω              ⁢                              xe2x80x83                            ⁢              t                        )                                                        Output          ⁢                      xe2x80x83                    ⁢          S          ⁢                      :                                                                                                            -                                      Γ                    ~                                                  ⁢                                  xe2x80x83                                ⁢                cos                ⁢                                  xe2x80x83                                ⁢                                  (                                      ω                    ⁢                                          xe2x80x83                                        ⁢                    t                                    )                                            =                                                                    "LeftBracketingBar"                                          Γ                      ~                                        "RightBracketingBar"                                    ⁢                                      xe2x80x83                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          ω                      ⁢                                              xe2x80x83                                            ⁢                      t                                        )                                                  +                ϕ                                      )                    ,                                with      ⁢              xe2x80x83            ⁢      tan      ⁢              xe2x80x83            ⁢              (                  ϕ          2                )              =                  1        -        Γ                    1        +        Γ            
Diode phase shifters essentially use voltage controlled varactors for continuous phase shifting, or switch operated PIN-diodes for digital phase shifting.
In principle, hybrid ring or square couplers or transformers may equally well be used. The band width of the phase shifters thus constituted is limited by the use of a coupler: these devices are typically narrow band, or operate at best on a two-octave band: xcfx89xe2x86x924xcfx89.
Vector modulators use the principle of addition of variable amplitude orthogonal vectors (I/Q).
In a vector modulator phase shifter, phase shifting between the input signal E and the output signal S is the result of recombining (11) two separately attenuated quadrature components. An example of a 0-90xc2x0 phase shifter with vector modulator is given in FIG. 2, with I and Q controls.
The record of the signals taken at the different points of the phase shifter is as follows:                     Input        ⁢                  xe2x80x83                ⁢        E        ⁢                  :                                    sin        ⁢                  xe2x80x83                ⁢                  (                      ω            ⁢                          xe2x80x83                        ⁢            t                    )                                        Output        ⁢                  xe2x80x83                ⁢        Oxc2x0        ⁢                  :                                    sin        ⁢                  xe2x80x83                ⁢                              (                          ω              ⁢                              xe2x80x83                            ⁢              t                        )                    /                      2                                                  Output        ⁢                  xe2x80x83                -                  90          ⁢          xc2x0          ⁢                      :                                                        sin          ⁢                      xe2x80x83                    ⁢                                    (                                                ω                  ⁢                                      xe2x80x83                                    ⁢                  t                                -                                  π                  /                  2                                            )                        /                          2                                      =                              -            cos                    ⁢                      xe2x80x83                    ⁢                                    (                              ω                ⁢                                  xe2x80x83                                ⁢                t                            )                        /                          2                                                              Point        ⁢                  xe2x80x83                ⁢        A        ⁢                  :                                    a        ⁢                  xe2x80x83                ⁢        sin        ⁢                  xe2x80x83                ⁢                              (                          ω              ⁢                              xe2x80x83                            ⁢              t                        )                    /                      2                                                  Point        ⁢                  xe2x80x83                ⁢        B        ⁢                  :                                              -          b                ⁢                  xe2x80x83                ⁢        cos        ⁢                  xe2x80x83                ⁢                              (                          ω              ⁢                              xe2x80x83                            ⁢              t                        )                    /                      2                                                  Output        ⁢                  xe2x80x83                ⁢        S        ⁢                  :                                                          [                                          a                ⁢                                  xe2x80x83                                ⁢                sin                ⁢                                  xe2x80x83                                ⁢                                  (                                      ω                    ⁢                                          xe2x80x83                                        ⁢                    t                                    )                                            +                              b                ⁢                                  xe2x80x83                                ⁢                cos                ⁢                                  xe2x80x83                                ⁢                                  (                                      ω                    ⁢                                          xe2x80x83                                        ⁢                    t                                    )                                                      ]                    /                      2                          =                  cos          ⁢                      xe2x80x83                    ⁢                      (                                          ω                ⁢                                  xe2x80x83                                ⁢                t                            +              ϕ                        )                              
if a=cos xcfx86 and b=sin xcfx86
These arrangements providing phase shifting over one quadrant, a 0-360xc2x0 phase shifter is obtained by combining 90xc2x0 hybrid couplers 10 and 180xc2x0 hybrid couplers 12, as shown in FIGS. 3A, 3B or 3C, or else by cascading four 0-90xc2x0 cells. The circuit bearing the reference 13 is a xc2xc phase splitter and the circuits bearing the reference 14 are 4:1 phase combiners.
These different phase shifters are all based on the generation of phase quadrature signals, by using and combining 90xc2x0 hybrid couplers. On principle, the 90xc2x0 hybrid couplers have a band width extending at most to about two octaves. It is therefore the same for the phase shifters thus constituted.
The article bearing the reference [1] at the end of the description describes structures of this type and particularly that of a vector modulator.
The object of the invention is to overcome the drawbacks of the prior art arrangements by proposing a new type of vector modulator.
The present invention concerns a vector modulator, characterised in that it includes:
an input stage providing the generation of a pseudo-basis of four vectors (xc2x1I, xc2x1Q), and comprising a multiphase filter;
an output stage making it possible to control the amplitude of the basis vectors, and to recombine them.
The input stage comprises successively:
a phase opposition signal generator;
a multiphase filter or network.
The output stage comprises:
four variable attenuators making it possible to achieve separate control of the amplitude of each of the basis vectors;
a common output providing the summation of the four quadrature channels.
To advantage the output stage includes two differential amplifiers isolating the variable attenuators from the multiphase filter/network. The quadrature channels are connected to the common output through buffer amplifier stages each followed by a summation capacitor.
The potential applications for this type of vector modulators are varied:
formation of beams (antenna arrays, antenna and synthetic aperture radar etc.);
high speed communications, frequency and angular multiplexing (satellite communications, digital television, WDM switchboard (see documents bearing the references [2] and [3] at the end of the description) etc.);
instrumentation (correlator, phase discriminator, vector analyser, etc.)
Such a modulator may be used, in fact, for the transmission of single side-band (SSB), or even suppressed carrier single side-band signals. Such transmission modes are appropriate for satellite communications, digital television, or telephony. The principle consists in transposing the frequency of the signal wanted to encode a carrier, so as to meet electromagnetic spectrum congestion or transmission quality criteria. It may also be used in antenna arrays or synthetic aperture radar: beam scanning by phase scanning.
In the case of digital television, there are two successive encodings: encoding the video image, then carrier modulation to 12 Ghz etc. By extrapolating such an embodiment, an analogous embodiment in optics may thus be conceived: hence the WDM modulation.
However, applications, functions or systems exploiting phase quadrature signals in a very wide frequency band (correlator, network analyser, phase discriminator, etc.) are particularly attractive.